I cannot download my emails from old iPad to new one.

Are you signed in to your email account on the new iPad?

If your primary email address isn't ALSO your AppleID, then you need to manually go into settings and sign in to that account to access those emails.

Settings

Mail

Accounts

If your account isn't there, you need to "Add Account".

If your account is there, you probably need to re-sign in.

There can be a delay on downloading ALL previous emails onto a new device.

What you're doing when you add an account to a device is, remotely, downloading data from a server, owned by Google, as an example--if your email account is "GMAIL". So this can take some time.

Hope this helps!